There has been known a torque sensor for detecting a shaft torque in an electric power steering device and the like. For example, in a torque sensor described in patent document 1, when torsion is caused in a torsion bar for coupling an input shaft to an output shaft, a magnetic sensor fixed to the torsion bar detects a magnetic flux generated by a change in a relative position in a peripheral direction between a multi-pole magnet and yokes to thereby detect a shaft torque. Here, the multi-pole magnet has N poles and S poles magnetized alternately at intervals of a given magnetizing angle in the peripheral direction. For example, the torque sensor described in the patent document 1 is provided with 12 pairs of N poles and 12 pairs of S poles that is, a total of 24 pairs of poles.
A torque sensor is a sensor for detecting a relative position in a peripheral direction of a multi-pole magnet and yokes. Hence, when the multi-pole magnet and the yokes are integrally turned with respect to a magnetic sensor, that is, when the relative position in the peripheral direction of the multi-pole magnet and the yokes is not changed, the output of the magnetic sensor is desired to be constant.
However, in reality, when the multi-pole magnet and the yokes are integrally turned in the torque sensor described in the patent document 1, an output is varied according to a turn angle. For example, in the case where the multi-pole magnet has 12 pairs of N poles and 12 pairs of S poles, there is caused a variation in output of 12 cycles for one turn. The variation in output becomes a factor of reducing a detection accuracy of the turn angle.
[Patent document 1] JP-A-2003-149062 (corresponding to US 2002/0189371)